​What does evidence tell us about the safety of swaddling?(Spoiler Alert: It "works." And parents should feel pretty good about wrapping babies up as long as they are sleeping on their backs.)​

​I’ve spent the last five years researching the history of Sudden Infant Death Syndrome (SIDS) for my PhD dissertation. Not surprisingly, no amount of research spared me from fear. Just like every other new parent, I was terrified at the prospect of SIDS. Even when my son was well past the peak age range for SIDS, I still worried. My work brought me no comfort; it just reminded me that there was precious little I could do to minimize the risk of SIDS.My forthcoming book, which details the history of the SIDS diagnosis, explains that one of the very few unanimously-accepted measures with incontrovertible powers to reduce a baby’s risk of SIDS is supine sleeping (back sleeping). (Another is not smoking. There are also lots of steps that can help parents establish a safe sleep environment, but their effects in terms of reducing SIDS are more difficult to calculate precisely. Besides that, some experts are not in agreement about what constitutes a “safe sleep environment.”) In terms of SIDS prevention, back sleeping’s effectiveness is undisputed. There was quite a hullaballoo over the 2016 meta-analysis on swaddling and SIDS published in Pediatrics. Initial news coverage reported the over-simplistic message that swaddling increased the risk for SIDS. Even reliable sources posed leading questions about whether swaddling was in fact a safe parenting habit. But the truth is, as more measured media analyses conveyed with witty taglines such as “About that Scary Swaddling Study” or “About that Alarming Study . . .,” the study’s actual, nuanced findings were hardly groundbreaking. The review was only “new” in the sense that it was recently published – rather than presenting unprecedented discoveries, the study reiterated what others have concluded for decades. In corroborating previous findings, it reinforced previously-available intel: all recent research on swaddling underscores the importance of supine sleeping.

Swaddling Past and PresentSwaddling is a challenging practice to study because it is so variably practiced across different cultures. But it does have a long history in human society – parents have been swaddling babies for thousands of years. Ancient Greeks and Romans swaddled their babies (though the Spartans did not). European peasants swaddled their babies in the Middle Ages. Native Americans swaddled babies. Up through the 1700s, most babies were swaddled, and not just for sleep.[1] Many societies harbored different ideas about why to swaddle babies. Some cultures did so for warmth, some for “shaping of the child’s body,” and others for its calming effects.[2] (One relied on swaddling to impede masturbation.[3]) Swaddling started to fall out of favor in western societies in the late 1700s. Borrowing rhetoric from the French and American Revolutions, early critics – philosophers more than physicians – rejected swaddling as an infringement upon infants’ freedom. Swaddling was confining. It was backward. It directly conflicted with the revolutionary principle of emancipation.[4] The case against swaddling swelled over the next hundred years to incorporate other concerns: it could cause physical damage, it was unhygienic, it was unkind, it was primitive. Over time, the once-ubiquitous practice of swaddling became obsolete in western, industrialized societies.[5] It stayed that way until the later-1900s. In the mid-twentieth century, most US parents saw swaddling as “antiquated,” cruel, and unnecessary. According to one report, in 1965, amid the Cold War, American (and Russian) parents expressed that “restraining an infant is . . . a significant step toward suppressing its freedom!” When advised, many parents were simply unwilling to use swaddling to calm their babies, and those who did were often uncomfortable with it.[6] In medical and lay literature, swaddling was so uncommon as to be infrequently discussed.

Make no Mistake: Swaddling Works Very few investigators studied swaddling before 2000. Before the mid-1960s, medical studies that did look at swaddling used animal subjects. Investigators in the early 1900s found that “immobilization was quite effective in inducing sleep in many species,” including frogs, guinea pigs, puppies, and kittens.[7]Some early studies to explore swaddling in humans reported that the restraint had a “’quieting effect.’” Swaddled babies slept more and cried less.[8] Scientists have corroborated those conclusions over again.Study after study shows that swaddling has calming and sleep-inducing effects for most babies. In 1965, researchers noted that swaddling “produced a tranquil, ‘co-operative’ state” akin to “pacification.”[9] Swaddling’s effectiveness was so clear that these investigators saw it as “useful clinically”: it curtailed babies’ “‘un-cooperativeness’” in the laboratory. “Swaddling clearly facilitates neonatal experimentation,” they wrote, “by maintaining a state of subdued physiologic activity by a procedure which is culturally acceptable.”[10] In other words, swaddling was an appropriate way to drug babies, and then study them, without literally drugging them. Again, studies continue to substantiate that swaddling calms babies and promotes sleep.[11] In a 2007 review that included “all known studies of swaddling,” authors explained that “overall, it is clear that swaddling stimulates sleep continuity.” It also decreases babies’ crying time “significantly.”[12]Swaddled babies wake less frequently, sleep for longer durations, and cry less.

What Doctors Know: Babies Shouldn’t Sleep ProneThe new Pediatrics study acknowledges that swaddling confers some broad benefits for families: it promotes sleep and reduces crying. But the analysis raised some concerns about whether swaddling is indeed safe. It incorporated four studies, and although the language may have come across as alarming, the findings were parallel with previous analyses. Where this article contributed a (somewhat) fresh perspective was on swaddling with regards to age and developmental milestones – specifically, it brought out the evidence that swaddling becomes less safe as babies reach about six months of age, or whenever they start learning to roll over. All of this goes back to prone sleeping. Swaddling becomes “risky” at six months or when babies start rolling because swaddled babies just becoming capable of rolling prone may struggle to maneuver their bodies or return to the supine position. In short, swaddling is a problem when combined with prone sleeping.[13]

We already knew this.

Consider these previous assessments about swaddling and sleep positioning:

In a 2007 review, authors concluded that advice about swaddling “should address the difference in SIDS risk associated with supine and prone sleeping.” They stated that “the combination of swaddling with prone position increases the risk of sudden infant death syndrome, which makes it necessary to warn parents to stop swaddling if infants attempt to turn.” In contrast, “swaddled infants in the supine position have a lower risk for SIDS,” they said – “evidence clearly shows that being supine and swaddled decreases the SIDS risk more than being supine without swaddling.” For infants placed to sleep on their backs, the investigators summarized: “swaddling seems to be protective. . . Up to a certain age, swaddling hinders turning prone, but on the other hand, when an infant is prone, his or her risk of SIDS significantly increases.”

(Side note: In some studies these discrepancies were drastic. In one, swaddled prone babies had a twelve times greater SIDS risk than nonswaddled prone babies.[15])

A 2009 study suggested that swaddling might increase the risk for SIDS because it so clearly depressed babies’ arousal thresholds, but still only concluded that swaddling potentially posed a risk for babies who were unaccustomed to swaddling. SIDS researcher Bradley Thach reflected that swaddling was only problematic when applied to prone babies, and that swaddling combined with supine sleeping had benefits for infants.[16]

A 2014 piece looking at swaddling-related injury and death incidents reported to the Consumer Safety Product Commission between 2004 and 2012 (there were 36) restated that sleeping prone and swaddled carried a ten times greater risk of death than sleeping prone and unswaddled. The authors emphasized that parents should discontinue swaddling when a baby begins learning to roll over, and that swaddling should only be employed in safe sleep environments.[17]

A separate study in 2016 also emphasized that swaddled babies are much more likely to die from SIDS when sleeping prone.[18]

So: the 2016 meta-analysis published in Pediatrics was important for adding to our pool of knowledge, but its conclusions were far from revolutionary.

O.K., But . . . All that being said, some skeptics still question whether swaddling’s effects are necessarily good for babies. Swaddling “works” in part by reducing startle responses during sleep. Parents can perceive swaddling’s effects as either “sleep promoting” or as “interfering with arousal,” because swaddling does both. For most (including me), extending sleep is a very desirable outcome, but not everyone thinks so. Critics argue that suppressing reflexes and extending sleep is detrimental for babies; swaddling “works like a drug,” writes Ralph Frenken. “It switches off the baby,” he says, and “‘works’ . . . because it forces the baby to sleep.”[19] Opponents of swaddling also point to other potential health hazards associated with the practice, but all those risks are only valid if swaddling in incorrectly employed. For example, the possibility of hip dysplasia “is related to the misapplied use” of swaddling.[20] Hyperthermia is a risk of swaddling only “when misapplied.”[21] Similarly, when swaddling is not routinely applied, but randomly used, it might carry more of a risk, in a similar vein to bed-sharing (which is particularly dangerous when practiced sporadically).[22]Experts agree: swaddling is only a risk when it’s done improperly. (Some observers have raised concerns that swaddling interferes with breastfeeding, but I don’t find this compelling, again unless swaddling is completely misused. Their logic is that routine swaddling, especially early on when feeding and milk supply are being established, swaddled babies might engage in less skin-to-skin contact and suffer decreased communication abilities with their mothers, and therefore be less likely to feed. The recommendation, though, is only to swaddle babies for sleep and to calm them down – not all the time.[23]) Proponents, most notably Harvey Karp, present a compelling rebuttal. Swaddling facilitates supine sleeping and may further prohibit infants from maneuvering into dangerous positions while they sleep.[24] It also helps that swaddling still so evidently works: swaddled babies sleep longer and cry less. Studies note that swaddling is thus associated with a “significant reduction of maternal anxiety, and an increase in parental satisfaction.”[25] While this might seem elementary, it could be much more important than it appears on the surface: parents who are better rested and less stressed out tend to be happier, and thus more engaged and satisfied with child care, and these types of benefits could have enormous (think ripple effect) down the line. Think “ripple effect”: because it is a relief to parents, swaddling could have the potential to minimize the chances for a whole cascade of health problems, ranging from postpartum depression to marital discord and unsafe sleep practices to smoking onset. (The AAP even advises swaddling “to reduce shaken baby syndrome.”)[26] Harvey Karp’s advice to parents: “keep on swaddling!”

Swaddling is a tool for parents. It is not safe because it is “natural” or because people have been doing it for centuries. It is not safe because it “works.” It is safe because medical study indicates it is (right now). Medicine is moving at such a past face these days that our perspective on swaddling could change at a moment’s notice – in theory, one study could wipe the slate clean. But the 2016 Pediatrics meta-analysis absolutely did not do this. It complemented what we already know: put babies to sleep on their backs, and start transitioning off swaddling as soon as babies can roll prone.